We now know that Pluto, the dwarf planet formerly known as a planet, has one more moon orbiting it. Using the Hubble Space telescope, astronomers have discovered Pluto's fifth moon.

NPR's Joe Palca filed this report for our Newscast unit:

"The new moon is tiny, something between 6 and 15 miles across. It showed up in nine separate images the space telescope made in the last month. The latest image came earlier this week.

"In 1978, astronomers found the first and largest of Pluto's moons. It's called Charon. Once the Hubble Space Telescope went into operation, astrononomers used it to find three other small moons of Pluto — Nix and Hydra in 2006 and one last year that the hasn't gotten a fancy name yet. It's just called P4. The new moon will be P5 — for now.

"Astronomers no longer consider Pluto a planet in our solar system. Instead, it's now referred to as a dwarf planet. But Pluto still draws astronomers' attention and a NASA probe will arrive at Pluto in 2015."

NASA says the discovery will help the New Horizons spacecraft navigate its way to the planet.

"Moving past the dwarf planet at a speed of 30,000 miles per hour, New Horizons could be destroyed in a collision with even a BB-shot-size piece of orbital debris," NASA said in a press release.